Develop Reference

How to download a json object as file?

I am currently trying to let the user of my website download a json object as a json-file.
With my following code i get the error message:
Error: Can't set headers after they are sent.
at SendStream.headersAlreadySent (\node_modules\send\index.js:390:13)
at SendStream.send (\node_modules\send\index.js:617:10)
at onstat (\node_modules\send\index.js:729:10)
at FSReqCallback.oncomplete (fs.js:168:5)
router.post('/about', ensureAuthenticated,
function (req, res, next) {
console.log(req.user);
var jsonVariable = JSON.stringify(req.user);
var path_tmp = create_tmp_file(jsonVariable);
res.download(path_tmp);
res.redirect('/about');
next();
}
);
Is there a better way to download a json object directly with no need to save it in the filesystem?

You can always inject some HTML into a page (or redirect to a page with some client-side JavaScript on it), and download it with the client. Just send the JSON string somehow to the new page you are redirecting to (it can even be a GET parameter), then download it with the following code (assuming the JSON string is in a variable called json):
var a = document.createElement("a")
a.href = URL.createObjectURL(
new Blob([json], {type:"application/json"})
)
a.download = "myFile.json"
a.click()

var jsonVariable = JSON.stringify(req.user);
var path_tmp = create_tmp_file(jsonVariable);
res.download(path_tmp);
Send the data with res.json and use content-disposition to make it a download.
res.set('Content-Disposition', 'attachment; filename=example.json')
res.json(req.user);
res.redirect('/about');
next();
And don't do that (which is the cause of the error). You are responding with a download. You can't say "Here is the file you asked for" while, at the same time say, "The file you asked for isn't here, go to this URL instead".

Download files from different protocols in JavaScript [duplicate]

I want to download file using absolute FTP URL, like ftp://host:port/dir/file.extension
I've tried node-libcurl, wget, wget-improved, request. All failed saying that the protocol must be either HTTP or HTTPS.
There are FTP clients available for Node (available on npmjs). But, as per their documentation, they require creating a connection to FTP Server, change directory and then download it.
Is there any simple solution?

I will outline a simple approach here (and no complete solution with code!). FTP is based upon TCP with a simple human readable protocol. In order to fetch a file from an FTP server you need to do the following:
Create a TCP socket using net.Socket
Use socket.connect to connect to your FTP server on port 21
Communicate with the server using socket.write to send data and socket.on('data') to read data
An example of FTPs protocol for a simple file retrieval is provided in this blog post and can be summarized as follows:
Connect to server using net.Socket.connect
Set user with USER command
Authenticate with PASS
Go to desired directory using CWD
Change to passive mode using PASV
Read server reply to find out IP and port to connect to in order to fetch the file
Open another socket on IP and port of previous step
Voilà!

Anyone wanting to have simple single line solution that in addition to FTP would also work with FTPS and SFTP, you can try ftp-any-get
import { getFile } from "#tpisto/ftp-any-get"
async function main() {
// Fetch from FTP server
let ftpFile = await getFile("ftp://demo:password#my-ftp-server.net/my-file.txt");
// Fetch from FTP server using TLS
let ftpsFile = await getFile("ftps://demo:password#my-ftp-server.net/my-file.txt");
// Fetch file using SFTP. SFTP runs over the SSH protocol.
let sftpFile = await getFile("sftp://demo:password#my-ftp-server.net/my-file.txt");
}
main();

You can use node-libcurl, I don't know exactly how you did it, but here is some working code.
var Curl = require( 'node-libcurl' ).Curl,
Easy = require( 'node-libcurl' ).Easy,
path = require( 'path' ),
fs = require( 'fs' );
var handle = new Easy(),
url = 'ftp://speedtest.tele2.net/1MB.zip',
// Download file to the path given as first argument
// or to a file named 1MB.zip on current dir
fileOutPath = process.argv[2] || path.join( process.cwd(), '1MB.zip' ),
fileOut = fs.openSync( fileOutPath, 'w+' );
handle.setOpt( Curl.option.URL, url );
handle.setOpt( Curl.option.WRITEFUNCTION, function( buff, nmemb, size ) {
var written = 0;
if ( fileOut ) {
written = fs.writeSync( fileOut, buff, 0, nmemb * size );
}
return written;
});
handle.perform();
fs.closeSync( fileOut );
The repository currently has one example showing how to download a file using wildcard matching, I just changed the URL to point directly at the file, and removed the WILDCARDMATCH and CHUNK_*_FUNCTION options.

Sending a file to the client from Node.js with Express

I have a unique situation in terms of difficulty.
I need to send HTML to the server, have the server convert the HTML to a PDF, send that PDF back to the client, and then download the PDF using client-side code.
I have to do it this way because I'm using client-side routing, so the only way I can access my endpoint that should perform this action is via a GET Request with Ajax or Fetch from client-side JavaScript. I am aware of res.sendFile(), but that attempts to render the file in the browser - I don't want that - rather, I want to be able to use client-side code to download the file.
Is it possible, then, to send a PDF file from temporary storage on the server down to the client, allowing client-side code to do whatever it wants to the file thereafter - in my case, downloading it?
I don't believe I have to provide any code because this is more of a theoretical question.

My issue stemmed from the fact that I could not just use res.sendFile() or res.download() from Express because the route was not being accessed by the browser URL bar, rather, my application uses client-side routing, and thus I had to make an HTTP GET Request via Fetch or XMLHttpRequest.
The second issue is that I needed to build the PDF file on the server based on an HTML string sent from the client - so again, I need to make a GET Request sending along a request body.
My solution, then, using Fetch, was to make the Get Request from the client:
fetch('/route' , {
method: 'GET',
body: 'My HTML String'
});
On the server, I have my code that converts the HTML string to a PDF, using the HTML-PDF Node module, and then, I convert that file to a Base64 String, setting the MIME Type and appending data:application/pdf;base64,.
app.get('/route', (req, res) => {
// Use req.body to build and save PDF to temp storage (os.tempdir())
// ...
fs.readFile('./myPDF.pdf', (err, data) => {
if (err) res.status(500).send(err);
res.contentType('application/pdf')
.send(`data:application/pdf;base64,${new Buffer.from(data).toString('base64')}`);
});
});
Back on the client, I have my aforementioned Fetch Request, meaning I just need to tack on the promise to get the response:
fetch('/route', {
method: 'POST',
body: 'My HTML String' // Would define object and stringify.
})
.then(res => res.text())
.then(base64String => {
// Now I just need to download the base64String as a PDF.
});
To make the download, I dynamically create an anchor tag, set its href attribute to the Base64 String in the response from the server, give it a title, and then programmatically click it:
const anchorTag = document.createElement('a');
anchorTag.href = base64String;
anchorTag.download = "My PDF File.pdf";
anchorTag.click();
So, all together and on the client:
fetch('/route', {
method: 'POST',
body: 'My HTML String' // Would define object and stringify.
})
.then(res => res.text())
.then(base64String => {
const anchorTag = document.createElement('a');
anchorTag.href = base64String;
anchorTag.download = "My PDF File.pdf";
anchorTag.click();
});
The solution for using an anchor tag to trigger the download came from another StackOverflow answer. It's also important to note that Base64 Encoding is not very efficient. Better solutions exist, but for my purposes, Base64 will work fine.
It is also imperative to note that Base64 Encoding is precisely that - an Encoding Scheme, not, I repeat, not an Encryption Scheme. So if your PDF files contain privileged information, you would likely want to add token authentication to the endpoint and encrypt the file.

send file from node to client for download

I am using an ajax call from browser
so, on button click
a function is called
for route '/file'
app.get('/filez',function(req,res){
var id = req.params.id;
console.log('id is : ',id);
var video = ytdl(url, { filter: (format) => format.container === 'mp4' })
.pipe(fs.createWriteStream('video.mp4'));
res.download('video.mp4');
now, the file is being downloaded to the server at the moment.
but what I want to do is to send the file so the client can download it from browser.
i dont want the file to be downloaded to the server.
Here's the ajax request I made from the browser using a button click.
and I want to get the file as the response which can be downloaded to the client computer.
function myAjaxCall(){
var xhr = new XMLHttpRequest();
xhr.onreadystatechange = function(){
if(xhr.readyState ===XMLHttpRequest.DONE && xhr.status ===200){
console.log('response has come',xhr.response);
return xhr.response;
}
};
xhr.open('GET','/filez',true);
xhr.send();
};
EXPLANATION : well, not really. i was thinking more along these lines - so on button click an ajax call is sent to server and it's supposed to get back a response. I want the file to be sent via this response.
so, how do I accomplish this?

pass the get request in a href tag and it will download the file to the client , you are writing the file in server side so it is being created their , you have to have the file been created on the server side and then serve the file through res.download to the client side and later delete the file from the server side to download the file in clinet side
suppose your url looks like http://getsomefile.com/xyz?newfile=video.mp4 then in your client sides a tag you can have this url as on some domain http://getsomefile.com with route xyz to serve the file
<a href="http://getsomefile.com/xyz?newfile=video.mp4" download>
where i am assuming on client side you have some route defined as
app.get('/xyz,function(req,res){
var file = req.query.newfile;
})
and then you can use fs.unlink to delete the files through a cron like or have a manual cleaner used or do something like this
app.get('/xyz', function(req, res){
var file = req.query.newfile
res.download(realFilepath, file , function(err) {
if (!err) {
fs.unlink(realFilepath);
}
});
});
realFilepath is the actual path of file kept in server , which you can gracefully delete after the file has been served.

NodeJS not trigger save file dialog in browser / EmberJS not receive file sent from server

My scenario:
I have an app written using MEEN stack (MySQL, ExpressJS, EmberJS, NodeJS). In a page, I have a form input. I am supposed to get the input data, send it to server, generate a PDF and display in EmberJS. The server is in NodeJS with ExpressJS, and the generated file is written to disk before getting sent to front-end.
My problem:
I cannot display the PDF file in EmberJS. Or rather, nothing is displayed. In my back-end with NodeJS and ExpressJS, I send a filestream of the PDF file back to EmberJS. Using a REST Client like Postman extension in Chrome, the dialog is called, and I can save the file. However, in EmberJS, no dialog appears, but I can see the content of the filestream using console.log in Chrome Dev Tools.
Why is it like this?
Below is my code for sending the file in NodeJS with ExpressJS.
generatePDF: function(req, res){
var details = req.body;
// #param details
// #return relative path to the file
inventoryController.generatePDF(details, function(relPath){
var filePath = path.resolve(relPath);
// This is the first method
// I explicitly specify the header for the Response Object
// and pipe the ReadableStream to the Response Object
// var name = path.basename(filePath);
// var mimeType = mime.lookup(filePath);
// res.setHeader('Content-disposition', 'attachment; filename=' + name);
// res.setHeader('Content-type', mimeType);
// var fileStream = fs.createReadStream(filePath);
// fileStream.pipe(res);
// This is the second method (currently being used)
// using sendfile() of ExpressJS, the header is automatically set
res.sendfile(filePath);
});
},
The code in Ember.js for sending details to server and getting data back.
var doc = {
// some attributes inside here
};
var url='/pdf';
var request = Ember.$.post(url, doc);
request.then(function(data){
if(data.status === 'ERR'){
// handling error
} else {
console.log('Successfully generated PDF.');
console.log(data); // I can see the filestream here
}
});

I think the problem lies that this isn't an Ember.js issue but a server issue, and how it's handled.
jQuery cannot save the file to disk, as it's a security risk. While extensions can override various security limitations, In Ember, or any other JavaScript framework (which uses jQuery) you cannot force a save as dialog as this is enforced by security. JavaScript cannot write to your local file format, (aside from html 5 local storage which is similar in many ways to cookies).
As such you cannot have a save as PDF. The only way to perhaps get that to work is allow the browser itself to capture the stream back and handle it:
You could try this plugin, but I'm not sure it works, and it's not recommended at all.
I'd recommend you just use a pure link from your browser and have the server send the file back in proper way, rather than an ajax call. You can either have a form submit it or a pure link with query string params.
Client Side:
<a href="/server/getFile?{"contentID"="123", "user" = "test#me"}>Get File</a>
or
<form action="/getFile" method="POST">
<input type="hidden" id="user" name="user" value="test#me" />
<input type="hidden" id="contentID" name="contentID" value="123" />
<input type="submit" value="Get File />
</form>
Server Side:
Add in the server the following headers:
res.setHeader('Content-disposition', 'attachment; filename=<file name.ext>');
It might be a wise idea to also add a mime-type:
res.setHeader('Content-type', '<type>/<subtype>');
full code:
var filename = path.basename(filePath);
res.setHeader('Content-disposition', 'attachment; filename='+ filename);
res.setHeader('Content-type', 'application/pdf');
// it's better to use a stream than read all the file into memory.
var filestream = fs.createReadStream(filePath);
filestream.pipe(res);
Or if you're using express you could use this helper
res.download(filePath)